In storage systems, the reliability and availability of data are ensured by replication. In the storage systems, technique for a redundant array of inexpensive disks (RAID) that ensures a certain level of reliability by adding a parity disk is used. In the storage systems, local parity calculated using partial data, not all data, is used to ensure a certain level of reliability.
Related technique is disclosed in Japanese Laid-open Patent Publication No. 8-249132 or Japanese Laid-open Patent Publication No. 8-185275.